The list has to be complete so that any reader can trace or find the sources referred to avoid what previous generations of students have named an ‘anthology of quotations’ in essays, research, etc. Own interpretations and ideas and conclusions are very important too. By giving credit to each source used, the reader sees what the author has been borrowed from other authors and what is the author’s own ideas and interpretations. The credits can include facts, ideas, opinions, images, etc. If the sources are not acknowledged, the writer is plagiarising which is a criminal offence. Students can even be expelled. Plagiarism is also known as ‘letter theft’.